The present invention relates to a clamp and, more particularly, to a clamp for clamping an adjustable bar hanger against a molded thermosetting plastic electrical wiring box without causing physical damage to the wiring box such as cracking or shattering.
Bar hangers for use with molded thermosetting plastic electrical wiring boxes for positioning the electrical wiring boxes with respect to supporting structures, for example, between studs or joists, are well known in the art. These bar hangers are normally mounted or secured to electrical wiring boxes, for example, in a factory assembly operation, and are commonly adjustable lengthwise in the field to permit installers in the field to accommodate the wiring boxes to variations in spacing between studs and joists. In one well known assembly of a thermosetting plastic electrical wiring box and bar hanger, the bar hanger is first positioned within a generally U-shaped portion of a clamp having side flanges, and the wiring box is positioned with respect to the clamp and bar hanger assembly so that the bar hanger is captured between the clamp and a rear wall of the wiring box with the flanges of the clamp being spaced a slight distance from the rear wall of the wiring box. At the same time, openings provided in the rear wall of the wiring box are aligned with corresponding threaded openings provided in the flanges of the clamp. Metal screws are then inserted by screw-insertion apparatus through the openings in the rear wall of the wiring box into the threaded openings in the clamp and a rotational torque is applied to the screws to thread the screws into the threaded openings in the flanges. As the screws are tightened, the clamp is drawn toward the rear wall of the wiring box and the bar hanger is caused to be clamped and retained in position against the wiring box. Desirably, the metal screws are tightened by an amount no more than is necessary to insure that the bar hanger will not become loosened and separate from the rest of the assembly during shipment of the assembly. Further, the screws should not be tightened so much as to cause the wiring box to crack or shatter at the points or region of entry of the screws into the wiring box, thereby rendering the wiring box non-usable.
While the above-described assembly operation has been used successfully for some time, it is possible, due to inherent variations in wiring boxes, clamps and bar hangers and inherent variations in assembly operations, for the screw-insertion apparatus to occasionally apply an excessive amount of force or torque to screws and cause a wiring box to be cracked, shattered, or otherwise damaged and thereby rendered non-usable. This result is possible since the screw-insertion apparatus, being mechanical and non-human in nature, is unable to exercise the degree of control and discretion over its screw-tightening operations that an installer would in the field. The present invention is directed to a solution to the above problem.